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Why is option a correct

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cauda equina syndrome absolute indication surgery lumbar disc prolapse guideline

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"cauda equina syndrome" AND surgery

I think you mean why option C is correct, not A.
C: Cauda equina syndrome is the absolute, urgent indication for surgery in a prolapsed lumbar disc because the disc is compressing multiple sacral nerve roots. Without rapid decompression, the patient may develop permanent:
  • Urinary retention or incontinence
  • Bowel dysfunction
  • Saddle anesthesia
  • Sexual dysfunction
  • Leg weakness
Urgent decompression gives the nerve roots the best chance of recovery. The AANS guidance on cauda equina syndrome describes it as requiring prompt surgery, generally as an emergency.
Why the others are not absolute indications:
  • A. Debilitating sciatica: surgery can be considered if pain remains severe despite adequate conservative treatment, but it is usually elective.
  • B. Sciatica not responding to epidural steroid injection: this supports considering elective surgery, not emergency surgery.
  • D. Progressive sensory loss: concerning and may justify surgery depending on severity and associated motor/bladder symptoms, but isolated sensory loss is not classically the single absolute indication in this exam framing. Progressive motor deficit is more urgent.
Textbook support: “Impairment of bowel and bladder function (cauda equina syndrome)” is listed as a surgical indication, with progressive neurological symptoms and failed conservative treatment as other, less absolute indications. Symptom to Diagnosis: An Evidence Based Guide, Treatment section, lines 1165-1193.
A nuance: in real practice, progressive major motor weakness also needs urgent spine assessment. But for this MCQ, cauda equina syndrome is the best and unequivocal answer.
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ASA practice advisory prevention perioperative peripheral neuropathies supine ulnar neuropathy forearm supination

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ulnar neuropathy AND perioperative positioning

Ulnar nerve (option B) is correct because it is very superficial at the elbow, where it passes behind the medial epicondyle in the ulnar groove/cubital tunnel.
In a supine anesthetized patient, an arm lying pronated on an armboard tends to put the medial elbow and ulnar groove against the supporting surface. This can cause prolonged external compression of the ulnar nerve, especially because the patient cannot feel discomfort and reposition themselves.
Supinating the forearm turns the ulnar groove away from the pressure point, reducing direct compression. It also helps avoid stretch/compression at the cubital tunnel.
So the sequence is:
Forearm pronation + pressure at medial elbow
→ compression of ulnar nerve in ulnar groove
→ postoperative ulnar neuropathy
→ numbness in little finger and ulnar half of ring finger, weak finger abduction/adduction in severe cases.
This is why perioperative positioning guidance recommends:
  • Arm on an armboard: keep the forearm supinated or neutral, with elbow padding.
  • Arm tucked at the side: keep the forearm neutral.
  • Avoid substantial elbow flexion, particularly prolonged flexion beyond 90 degrees.
The ASA positioning advisory likewise recommends a supinated or neutral forearm position on an armboard to reduce pressure over the ulnar groove, as summarized in the ASA practice advisory.
The other choices are not the classic positioning neuropathy prevented by forearm supination:
  • Radial nerve: vulnerable mainly to compression in the spiral groove of the humerus.
  • Posterior interosseous nerve: compressed near the radial head/supinator.
  • Anterior interosseous nerve: a branch of median nerve, usually affected by forearm compression or pathology, not medial-elbow pressure.
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